1. Technical field of the Invention
The invention relates to elevator dispatching and, more particularly, to improvements in estimating remaining response time (RRT) to answer a hall call.
2. Discussion of Related Art
Remaining response time (RRT) is the amount of time that a given elevator will require to reach a given hall call floor. For example, a car in the down direction and parked at floor 9 might require 6.0 seconds to respond to a newly registered down hall call on floor 7; in that case it is said that the RRT equals 6.0 seconds. The RRT for another car presently on floor 16 would be much longer. Another important illustration of RRT is the case where a car is in the process of responding to a hall call that has already been waiting for some time. Here, the RRT is the time from now until the car arrives at the hall call floor. The RRT is a key concept in dispatching decisions.
Co-owned US patents pertaining to RRT include, among others, U.S. Pat. Nos. 5,146,053; 5,388,668; 5,427,206; and 5,672,853. Clearly, accuracy of an estimation procedure for RRT is critical, especially as it is applied to dispatchers with ECA (Early Car Announcement: See U.S. Pat. No. 5,338,904).
An especially bad scenario occurs when a car has been assigned to a hall call based on an estimate that the RRT would be short (say 20 seconds), only to discover a few seconds later that the actual response time will be excessively long (say 90 seconds). With a system of car announcement commonly used in North America, the hall call would be reassigned to another car. With instantaneous car assignment(ICA) systems commonly used elsewhere, however, no such reassignment is permitted. A class of problems that is susceptible to such gross errors of RRT estimation leading to poor assignments is illustrated in FIG. 1, where a down traveling car is a candidate for assignment to a down hall call above the car (symbolized by inverted delta). The straightforward calculation of RRT would be something like 21 seconds as follows: travel from 2 to L (five seconds) plus stop at L (10 seconds) plus travel from L to 3 (six seconds). However, between the assignment of the car to the hall call and the car's answering the call (i.e., reaching the hall call floor) the car will often become burdened with commitments that will delay the car's response to the hall call. For this example, the lobby floor forms a "horizon" beyond which the car cannot "see." What is waiting over the horizon is the potential generation of car calls due to the extra level of passenger traffic at the lobby. During the time that the car is stopped at the lobby, people will board the car and enter car calls (symbolized by bullets) that will require the car to travel up into the building, far beyond floor 3, as shown in FIG. 2. For this situation, there is a need to add some number of seconds to the straightforward RRT value to account for the extra time that will often be required.